Electron discharge device and associated circuit



s. HiLL March 18; 1947.

ELECTROf I nlscnmes DEVICE AND ASSOCIATED CIRCUIT File d May 1, 1945 0vVEA/TOP ab A-rrop/vEy Patented Mar. 18;, 1947 ELECTRON DISC tranceDEVICE AND ASSQCIATEDGIECUIT Stanley Hill, HestonfEngland, assignor toElectric & Musical Industries Limited, Hayes, Middlesex,

England, a company of Great Btita'in- Application May 1, 1943, SerialNo. 485,2 90 In Great Britain January 17, 1941 This invention relates toelectron discharge de- '5 further electrode between vices of thevelocity-modulation type employing hollow resonators and in which astream of electrons after having been velocity-modulated by passingthrough the resonator gap is adapted to be 3 Claims. (Cl. 31 5 -5)reflected by the provision of a reflecting electrode It is found,however, that the efficiency of a device of this type when operating asa generator of oscillation is rather low when operating with a lowcurrent and a high resonator potential and this is to some extent due tothe unsuitable poten- I, tial distribution of somewhat parabolic form inthe space between the resonator and the reflecting electrode wherebyonly a small degree of bunching occurs. I have found that the efflciencyof devices of the kind referred to can'be substantially improved byarranging that the field gradient in the space between the resonator andthe reflecting electrode has a positive or zero value over at least halfthe distance between the middle of the gap in the resonator andthe zeroequi-potential surface which is setup in operation between the resonatorand the reflecting electrode. The field gradient has the positive andnegative values referred to herein when said values are derived from aplot of thepotential distribution taken from the resonator to therefleeting electrode. i

According, therefore, to one feature of the invention I provide anelectron discharge device and a circuit of the type referred to whereinthe construction and arrangement of the electrodes are such that withsuitable potentials applied to the electrodes the field gradient alongthe path of theelectrons between the resonator and the reflectingelectrode has a positive or zero value over at least half the distancebetween the middle of the gap in the resonator and the zero equipotential surfacewhich is set up in the space between the resonator andthe reflecting electrode. Such a field gradient can be obtainedin avariety of ways, such as by shaping the reflecting electhe resonator andthe reflectingelectrode.

' The shape of the further electrode will depend onthe form of theelectron beamand in cases where the electron beamis ofasubstantially'circular'forin in cross-section, the further electrodemay-comprise a cylinder-or disc surrounding the beam. Other forms ofrefiectingelectrodescan beemployeddepending on the shape of theelectronbeam as will hereinafter be referred to. A potentialdistribution between "the resonator and the "reflecting-electrode whichpassesfrom a positive value atthe-resonator- -linearly with distancethrough zero-to a negative-value at the reflecting electrode provides aconstant potential gradient'throughout thespa'ce and hence the fieldgradient is always'zero. Sucha new gradient aflords" a muchbetter resultthan is the case if the-fieldg-radientis positive. A zero field gradientcan be approximated in practice by providing a large number of furtherelectrodesbetween the resonator'and the reflecting electrodathe furtherelectrodes being maintained at slightly different potentials passingfroma positive value at the further electrode closest to the resonator to anegative value at the further electrode-closest to thereflectingtelectrode, the potentials applied to the furtherelectrodesbeing so chosen that the potential distribution .issubstantially linear. Such an arrangement is, however, .cumbersomeinpractice and hence; for practical purposes, it is preferred toiemployaeminimum number of further electrodes.

In order that the said invention may be clearly understood andreadilycarried into effect,sit will now be more :fully described with referenceto the accompanying drawing which illustrates one form of dischargedevice provided with a further electro'de in accordance with,theinvention:

As shownin the drawingwthe reference numeral I indicatesthe evacuatedenvelope of the device having at one-ends. cathode 2 'whichis arrangedtoproject azbeam of electronsthrough the gap 3 in a hollowresonator flytheelectron stream passing through the resonator being directed towards areflecting electrode -51 Thehollowres'on'ator 4 is of toroidalformhaving the cross-section shown and is arranged partly within andp'artly outside the evacuated "envelope 1. 'In accordance withone'feature of the invention a further electrode 6 is provided arrangedbetween the resonator 4 and the electrode 5. When operating the deviceshown in the drawing as a generator of self-maintained oscillations, alow current of about 10 to milliamperes is employed and the resonator 4is maintained at a high potential of about 1000 to 2000 volts positivewith respect to the cathode 2 and the reflecting electrode 5 at apotential of 100-200 volts negative with respect to the cathode thefurther electrode 6 being maintained at a potential, preferably at anegative potential, intermediate the potentials applied to the resonatorl and the reflecting electrode 5. The field gradient is changed byintroduction of the electrode 6 which sets up between the resonator 4and the reflecting electrode 5 equi-potential surfaces which are,concave facing the resonator '4, as indicated by the dotted lines,these concave equi-potential surfaces extending over a distance alongthe path of the electrons which is longer than the distance over whichconcave surfaces would be set up in the absence of the further electrode6, so that the field gradient has a positive value over at least halfthe distance along the path of the electrons between the middle of thegap 3 in the resonator and the zero equi-potential surface which is setup between the resonator and reflecting electrode. The zeroequi-potential surface referred to herein is the equi-potential surfacehaving the potential of the cathode of the device. In practice, theresonator may be maintained at earth potential and the cathode at about1000 volts negative with respect to earth and the reflecting electrodeat about 1100 or 1200 volts negative with respect to earth. In this casethe zero equi-potential surface between the resonator and reflectingelectrode will be the 1000 volts negative equi-potential with respect toearth. In some of the previously proposed resonators the wall of theresonator adjacent the reflecting electrode is symmetrical with the walladjacent the cathode and such a construction of resonator is also foundto impair the efficiency of operation owing to the re-entrant form ofthe rear wall. It will be observed that in the construction shown in thedrawing the rear wall of the resonator is substantially flat in thevicinity of the reflecting electrode and this flattening of the rearwall of the resonator is also found to effect an improvement on the(efficiency of operation.

The reflecting electrode 5 in the example shown is substantially flatalthough, in some cases, the reflecting electrode 5 may be of concaveform with the concavity facing the resonator.

The disposition of the electrode 6 in relation to the resonator 4 andreflecting electrode 5 and the dimensions of the electrode 6 are notcritical and in one form of the invention, given purely by way ofexample, ina case where theresonator dis tuned to operate at awavelength of 9 centi metres, the electrode 6 may comprise a cylinder,about 6 millimetres in diameter and the length of the cylinder may beabout 3 millimetres. The distance between the rear wall of the resonatorand the reflecting electrode may be about 5 or 6 millimetres. Thediameter of the apertures forming the gap in the resonator 4 may beabout 3 or 4 millimetres in diameter.

The device shown is intended to be employed with an electron beam of asubstantially circular form in cross section and in this case thefurther electrode 6 will also preferably be of circular form in crosssection. Instead, however, of employing a cylindrical electrode one ormore apertured diaphragms may be employed, these apertured diaphragmsalso serving to provide the required field gradients and by employingmore than one apertured diaphragm or more than one of the cylindricalelectrodes, shorter in length than that mentioned above, and maintainingthese electrodes at potentials which are progressively more negativetowards the reflecting electrode 5, the distance along the path of theelectrons over which the concave equi-potential surfaces are set up canbe increased, and the field gradient can be caused to approach closer tothe zero field gradient referred to above.

' The features of the present invention can also be applied to electrondischarge devices which employ ribbon-shaped beams. In this case thefurther electrode 6 will be shaped appropriately and may comprise acylinder having an elongated cross-section or a diaphragm having anelongated opening or, alternatively, may comprise a pair of flat stripslying substantially parallel to the major axis of the ribbon-shaped beamas viewed in cross section. The pair of strips will be maintained at thesame potential.

The features of the invention can also be applied to electron dischargedevices where an electron stream flows radially through an annular gapin a resonator. In this case the further electrode may comprise a pairof rings lying one on each side of the beam.

What I claim is:

1. A high frequency apparatus including a source of electrons and anelectrode toward which said electrons are to be directed, and a cavityresonator positioned between said source of electrons and saidelectrode, electrode means between said resonator and said electrode,means including a source of voltage and conductors connected betweensaid source of voltage and said resonator, said electrode and saidelectrode means for maintaining said resonator at a high positivepotential with respect to said cathode, said electrode at a negativepotential with respect to said cathode, and said electrode means at apotential intermediate that of the resonator and said electrode.

2. A high frequency apparatus including a source of electrons and anelectrode toward which said electrons are to be directed, and a cavityresonator positioned between said source of electrons and saidelectrode, electrode means between said resonator and said electrode,said electrode means comprising a tubular ring-like member closelysurrounding the electron path and spaced closely adjacent said resonatorand said electrode, means including a source of voltage and conductorsconnected between said source of voltage and said resonator, electrodeand electrode means for maintaining said resonator at a high positivepotential with respect to said cathode, and said electrode at a negativepotential with respect to said cathode, and said electrode means at apotential intermediate that of the resonator and said electrode.

3. A high frequency apparatus includin an electron discharge devicehaving a source of electrons and an electrode toward which saidelectrons are to be directed, a cavity resonator positioned between saidcathode and said electrode and through which electrons are directedduring operation of said apparatus, and only a single tubular electrodemeans positioned between said resonator and said electrode and throughwhich the path of the electrons extends between said resonator and saidelectrode and closely sur- ,5 rounding said path, said resonator havinga flat surface adjacent said tubular electrode means and transverse tothe path of the electrons, and a voltage source having conductorsconnected between said voltage source, said resonator, electrode andelectrode means for applying a positive potential to said resonator anda negative potential to said electrode with respect to said cathode, anda potential intermediate said two potentials to said tubular electrodemeans, whereby the field gradient along the path of the electronsbetween the resonator and the electrode has a value other than negativeat least half the distance between the middle of the gap in theresonator and the zero equipotential surface 15 2,190 511 which is setup in the space between the resonator and the reflecting electrode.

STANLEY HILL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS '10 Number Name Date 2,325,865 Litton Aug. 3, 19432,242,249 Varian et al May 20, 1941 2,329,778 Nergaard Sept. 21, 19432,293,151 Linder Aug. 18, 1942 Cage Feb, 13, 1940

